This application is the U.S. National Stage of International Application No. PCT/US2014/039079, filed May 22, 2014, entitled “Orthogonal Superposition Rheometer,” which claims priority to U.S. Provisional Application No. 61/826,576, filed May 23, 2013, both of which are incorporated by reference herein in their entireties.
The present embodiments relate to rotational rheometers that may be used to measure rheological properties of materials such as the viscosity or modulus of the materials.
Rheometers may be used to measure the properties of materials such as oils, dispersions, suspensions, emulsions, adhesives, biological fluids, polymers, gels, pastes, slurries, melts, resins, powders or mixtures of the foregoing. Specific examples of such materials include asphalt, chocolate, blood, drilling mud, lubricants, oils, greases, photoresists, liquid crystals, liquid cements, elastomers, thermoplastic polymers and coatings.
As used herein, the term “rheometer” shall include rheometers, viscometers, viscosimeters and any other instrument that may be used to measure the viscoelastic properties of fluids or powders. Also, as used herein, the term “fluid” shall include liquids, oils, dispersions, suspensions, emulsions, adhesives, biological fluids, polymers, gels, powders, pastes, slurries, melts, resins and mixtures of any of these materials, as well as any other materials that may be characterized according to their viscoelastic properties.
Rheological measurements in rotational rheometers are performed by applying a stress or deformation (rate) in a rotational direction. Rotational rheometers may apply a predetermined torque to a material in a rotational direction, and measure the resulting displacement of the material under test. Alternatively, they may measure the torque required to obtain a predetermined displacement.
In an orthogonal superposition rotational rheometer, an additional shear deformation (rate) or stress is applied in a second direction, normal to the rotational direction. This may be used, for example, to measure the effect of a strong shear flow on the rheological behavior of the material.
A test module for an orthogonal superposition rheometer may have a double wall cup retaining the test fluid and a cylindrical bob. The cylindrical bob is inserted between the inner and outer wall of the cup, providing the inner and outer circular shear surfaces for the fluid when either the cup or the cylindrical bob performs a rotational and/or an axial movement. In a typical test setup the cylindrical bob is attached to a torque/force transducer, but the bob could also be attached to a rotational/linear actuator.